Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 21, 2004
Publication Date: November 1, 2004
Citation: Moallem, U., Dahl, G.E., Duffey, E.K., Capuco, A.V., Mcleod, K.R., Baldwin, R.L., Erdman, R.A. 2004. Bovine somatotropin and rumen undergradable protein effects in prepubertal heifers: Effects on body composition and organ tissue weights. Journal of Dairy Science. 87(11):3869-3880.
Interpretive Summary: Effects of recombinant bovine somatotropin (bST) and dietary rumen undegradable protein (RUP) on heifer growth were evaluated. Data suggested that bST and, to a smaller extent, RUP can be used to increase growth rates of dairy heifers without fattening. Increased deposition of body protein and ash indicate that rates of skeletal growth can be enhanced without the detrimental effects of fattening usually associated with accelerated growth. Relative changes in growth of visceral organs appeared to support increased rates of body growth with bST administration. This suggests that there is coordination between need for metabolites and growth of the visceral and digestive tract organs needed to support the need. In contrast to previous experiments where increased growth has been achieved by increasing energy intake and fat deposition, heifers treated with bST and RUP increased growth rates without body fattening. Hormonal and nutritional manipulation can increase skeletal growth rates of prepubertal heifers to enhance body growth without increasing fat deposition.
The objectives of this study were to determine the effects of recombinant bovine somatotropin (bST) and added dietary rumen undegradable protein (RUP) on organ and tissue weights and body composition in growing dairy heifers. Twenty-four heifers (6 per treatment group) were randomly assigned to treatments consisting of 0.1 mg/kg body weight per day of bST and 2% added dietary RUP (dry matter basis) applied in a 2x2 factorial design. Eight heifers were slaughtered at 3 mo of age to determine pre-treatment body composition. Twenty-four heifers, six per treatment group (3 each at 5 and 10 mo of age) were slaughtered. There was a trend for increased live and empty body weights (EBW), carcass and non-carcass components, for heifers treated with bST or fed RUP. Added RUP increased rumen and reticulum weights whereas administration of bST tended to increase the weights of small and large intestine at 10 mo of age by 22% and 26%, respectively. Spleen, heart, and kidney weights at 10 mo of age were increased 36, 28 and 23% for bST treatments respectively, compared with controls. Rates of ash and protein deposition between 3 and 10 mo of age were increased by bST by 7.2g/d and 28.9 g/d, respectively, while no treatment differences were observed for rates of fat and energy deposition. Bovine somatotropin significantly altered the metabolism of growing heifers in a manner that led to increased protein and ash deposition, and tended to reduce fat percentage, and there was a similar tendency observed with added RUP. This suggests that nutritional and endocrine manipulations could increase growth rates of skeletal and lean tissues without increasing fat deposition in prepubertal dairy heifers.